1. Field of the Invention
The invention relates generally to the field of telecommunications, and more particularly to mechanisms for providing outer loop power control in a wireless communication system having multiple channels with varying channel qualities.
2. Related Art
Wireless communication technologies are rapidly advancing, and wireless communication systems are utilized to provide a larger and larger portion of the communications capacity that is currently available to users. This is true despite the additional technological impediments that are faced in implementing a wireless communication system, as compared to a wireline system. For instance, wireless communication systems must deal with issues relating to power control between a base station and its mobile stations in order to maximize the performance of the system, whereas a wireline system does not.
One type of wireless communication system comprises a cellular CDMA (code division multiple access) system which is configured to support voice and data communications. This system may have multiple base stations which communicate via wireless channels with multiple mobile stations. (The base stations are also typically coupled via wireline networks to various other systems, such as a public switched telephone network.) Each base station communicates with a set of mobile stations that are within a sector corresponding to the base station. This base station is responsible for controlling power in communications between the base station and the mobile stations in order to minimize interference and maximize throughput, as well as enabling the mobile stations to conserve energy and thereby extend the amount of time during which they can be used.
Power control between the base station and a mobile station in this type of system is typically based upon an error rate associated with communications between the base station and the mobile station. Ideally, the power level of the transmissions from the mobile station to the base station is set to a level that results in a predetermined frame error rate. For example, each time a frame of data is successfully received by the base station from the mobile station, the base station may direct the mobile station to reduce its power by a certain amount. In other words, the mobile station decrements its power level. If on the other hand, a received frame of data contains errors, the base station may direct the mobile station to increase its power by a certain amount (i.e., increment its power level). In this manner, the power level of the mobile station is adjusted to a power level at which the predetermined, acceptable error rate is maintained.
This method for power control, however, is based on a single channel and does not account for the varying transmission characteristics of multiple reverse-link channels. In systems having multiple channels, the power levels of the different channels may be tied to each other so that optimizing the power level based upon the error rate associated with one channel may provide acceptable performance on that particular channel, but may at the same time provide an unsatisfactory level of performance on one or more of the other channels. While the adjustment of the power mobile may take into account the performance of multiple channels, there will almost certainly be some channels for which the power level is too low and some for which the power level is too high.